The intent is to elaborate the pathogenesis of injury and chronic disease that may be induced by exposure to the atmospheric oxidants NO2 and O3. Both the influence of realistic ambient conditions of photochemical smog and of the inhalation of tobacco smoke are considered. Use is made of the rat model of experimental emphysema in which to study the sequence of events leading to the overt disease. The several approaches used to describe the pathogenesis include clinical evaluation, respiratory physiology, blood gas analyses, tissue pathology, electron microscopy, quantitative cell renewal studies, biochemistry, and histochemistry. Animals are studied at all ages from birth to old age. BIBLIOGRAPHIC REFERENCES: M. J. Evans, L. V. Johnson, R. J. Stephens, and G. Freeman. Cell renewal in lungs of rats exposed to low levels of ozone. Exp. Mol. Pathol. 24, 78-83 (1976). M. J. Evans, R. J. Stephens, and G. Freeman. Renewal of pulmonary epithelium following oxidant injury. Pneumonology 153, 145 (1976).